Rankine (°R)
The Rankine scale, symbol °R, was developed in 1859 by the Scottish engineer William John Macquorn Rankine. Consistently, like Kelvin, it starts at absolute zero but uses Fahrenheit-sized degrees instead of Celsius. This makes Rankine particularly useful in engineering fields within the United States, especially in thermodynamics, aerospace, and combustion studies. One Rankine equals 1°F increment, with 0°R corresponding to absolute zero. Although less common in everyday life, the Rankine scale remains important in theoretical and applied engineering, where calculations are based on the Fahrenheit system.
Kelvin (K)
The Kelvin (K) is the SI base unit for temperature, named after the Scottish physicist William Thomson, known as Lord Kelvin, who introduced this scale in the 19th century. The scale begins at absolute zero, the point at which particles possess minimal thermal energy. Unlike Celsius or Fahrenheit, the Kelvin scale starts at an absolute reference, eliminating negative values and making it particularly useful in scientific research and engineering. Since 2019, the Kelvin has been officially tied to the Boltzmann constant, ensuring a measurement standard based on fundamental physical properties. It is extensively used in disciplines such as physics, chemistry, astronomy, and cryogenics where exact temperature readings are necessary.